Bodies believed to be those of the six missing Russian crew members were found inside a Cambodia- registered freighter that caught fire early Thursday in a port in Japan’s northern prefecture of Hokkaido, according to local media.

Rescuers, including firefighters and Japanese Coast Guard, took about 11 hours to put out the fire since they received an emergency call at around 1:45 a.m. local time, Japan’s Kyodo News Agency cited local authorities as saying.

Three Russian sailors among a total of 18 crew members were rescued and have been sent to hospital without serious injuries, according to the report.

The rest sailors, including another five more Russian crew members boarded at the Wakkanai port, were confirmed safe.

About two thirds of the ship’s interior was burned, said local officials, adding it is difficult to discharge large amounts of water at once to put out the fire as the vessel’s interior was divided into many small sessions.

The 497-ton crab freighter docked at the port Tuesday with 14 Russian and four Ukrainian crew members on board and scheduled to leave Thursday.